1. Technical Field
The field relates to flexural disk transducers and more particularly to a shell or enclosure providing improved efficiency in operation.
2. Description of the Problem
Flexural disk transducers are usually constructed as metal/ceramic bi-laminar (or tri-laminar), vibratile electroacoustic transducers. Early versions were placed in housings in which they were mounted along their perimeters and which included an acoustic shield which left only the central portion of one major transducer surface of the piezoelectric ceramic exposed to the transmission medium such as water or air. This was done due to inner and outer portions of the disk operating out of phase with one another when the disk was operated in its free fundamental resonance mode. Shielding a portion of the disk mitigated destructive interference between the different sections of the disk.
Use of such shields was known to reduce the efficiency of such devices. This loss of efficiency was addressed in U.S. Pat. No. 4,190,783 which was directed to device for use in air in which the shield or plate was displaced from the transducer surface and sized so that sound produced along the peripheral edge reached a central aperture in phase with sound produced at the center of the device. The plate functioned to introduce a time delay for the sound generated by the peripheral portions of the disk allowing them to be constructively added to vibrations generated in the center of the disk. In this way most of the sound energy produced along one face of a disk could be captured.
Flexural disk transducers have been applied to underwater applications as well, particularly as high frequency acoustical sources. In such applications it has been supported along its edges so that the disk vibrates in a flexural mode similar to the bottom of an oil-can when depressed to force out oil.